Filter circulating type sewage disposal apparatus

ABSTRACT

The present invention relates to a sewage disposal apparatus employing large buoyant filter media and is directed to prevent effectively clogging in these filter media. The intended object of the invention can be attained by circulating the filter media by a circulation arrangement to allow the filter bed as a whole to flow very calmly, and more efficiently by removing sludge deposited on the filter media utilizing the circulatory movement of the filter media.

TECHNICAL FIELD

The present invention relates to improvements in a sewage disposalapparatus employing a buoyant filter system, particularly large buoyantfilter media having a diameter of several to ten centimeters or so,which apparatus is suitably employed for purifying a large capacity ofwater, for example for purifying river water.

BACKGROUND ART

The sewage disposal apparatus employing large filter media has a filterbed formed by an assembly of a multiplicity of buoyant filter media in aseptic tank, with aerobic or anaerobic bacteria which are effective forsewage treatment being allowed to proliferate on this filter bed, andsewage is designed to be purified gradually as it is allowed to flowslowly downstream in the septic tank in contact with the filter media inthe filter bed.

However, in the prior art sewage disposal apparatus employing largefilter media, the filter bed is fixed, so that sludge clogging occurs ineach medium or between the media to reduce purifying capacity of theapparatus after a predetermined amount of treatment. In order toeliminate such reduction in the purifying capacity, the filter media inthe apparatus must entirely be replaced with new ones or cleaned and theapparatus must be overhauled periodically, leading to great operationcost elevation.

There are other conventional methods which prevent such clogging byemploying filter media hard to be clogged or by pretreating sewage toreduce the sludge concentration thereof, followed by treatment of thediluted sewage for final sewage disposal treatment.

However, the conventional method employing pretreatment of sewagerequires considerably troublesome work for the pretreatment itself, andall what it can do is to delay clogging. Thus, it is impossible tothoroughly obviate clogging itself, and eventually, the filter mediamust be replaced with new ones or cleaned periodically, which requirestroublesome, heavy work.

Meanwhile, a buoyant, spherical filter medium hard to agglomerate itselfwith others is disclosed, for example, in Japanese Patent No. 1343032(Japanese Patent Publication (Kokoku) No. 61-2440). Such contrivance mayimpart a high level of clogging inhibitory capacity to the mediumitself, but it is not sufficient to completely eliminate clogging.

The present invention has been made in view of such problems in theprior art, and it is therefore an object of the invention to provide asewage disposal apparatus, in which a gentle flow of the filter bed isprovided by a circulatory movement of the filter media, while the sewageunder purification treatment flowing through the filter bed is adaptednot to be affected, or the flakes of sludge coming off from the filtermedia are prevented from diffusing into the treated water as the filtermedia are moved, and further the filter media are cleaned by utilizingthis circulatory movement thereof whereby to prevent effectively theclogging of the filter medium as well as to constantly enable efficientsewage disposal treatment.

DISCLOSURE OF THE INVENTION

The objects of the invention can be attained by a circulating filtertype sewage disposal apparatus having a septic tank containing manybuoyant filter media to form a filter bed consisting of an assembly ofthese filter media, in which sewage is purified by the action ofbacteria proliferating on the filter bed as the sewage is allowed toflow downstream in contact with the filter bed in the septic tank, saidapparatus comprising:

a filter moving means for returning the filter media to the upstreamextremity from the downstream extremity of the septic tank; and

a first current forming means for generating a vortex current and asecond current forming means for generating a straight jet streamcurrent, at the upstream extremity of the septic tank;

wherein the filter media separated from the filter bed at the downstreamextremity of the septic tank are brought back to the upstream extremityof the septic tank by the filter moving means, while the filter mediabrought back to the upstream extremity are returned to the bottom layerof the filter bed with the aid of the vortex current formed by the firstcurrent forming means and the straight jet stream current formed by thesecond current forming means.

The sewage disposal apparatus of the invention is developed based on thefinding that clogging can effectively be prevented so long as the filtermedia are constantly in motion, but if the filter media are moveddisorderly, it allows diffusion of the sludge flakes coming off from thefilter media throughout the septic tank.

Accordingly, the sewage disposal apparatus of the invention caneffectively prevent clogging in the filter media and constantly enablesefficient purification of sewage by securing constant and orderlymovement of the filter media which proved to be a prerequisite accordingto the above finding.

In other words, the cycle of separating the filter media reached thedownstream extremity of the apparatus and returning them to the filterbed at the upstream extremity is repeated continuously to allow thefilter bed to flow calmly as if it were a glacier as the filter mediaare circulated, and thus clogging of the filter media can effectively beprevented. Meanwhile, since the filter media are adapted to be rotatedbeing involved in the vortex current formed by the first current formingmeans when the filter media are returned to the filter bed at theupstream extremity, cleaning of the filter media can also be carried outeffectively by this rotational movement. Besides, the filter media areallowed to perform such movement as to allow coming off of the sludgedeposited thereon substantially only at the upstream extremity of theseptic tank, or at the portion of the untreated sewage where the sludgemay not give adverse effect to the sewage treatment, causing noreduction in the purification efficiency attributable to diffusion ofsuch sludge flakes.

Use of a water current as the filter moving means enables more rationaldesigning of the apparatus. More specifically, if a circulation passageis provided in the septic tank to cause a water current, communicatingto the inside of the septic tank, to flow from the downstream extremityto the upstream extremity of the septic tank and to allow the filtermedia to flow on the water current in this circulation passage,separation of the filter media from the filter bed can be carried outmore effectively and efficiently, and also possible causes of troublescan be reduced in the filter moving means.

When the filter media are allowed to move using the water current in thecirculation passage, a sludge removing means may be disposed forremoving sludge from the filter media in this passage. Such arrangementcan further minimize contamination of the treated water with the sludgeflakes coming off from the filter media, and thus purificationefficiency can further be enhanced.

As the sludge removing means in the circulation passage, a vortexcurrent formed therein can be employed. Such means is of a very simplestructure and high efficiency.

The septic tank may be of a shuttle type structure where the upstreamextremity and the downstream extremity are located side by side. Suchshuttle type structure can improve utilization of the installation spacein the case of an elongated septic tank.

A conveyor having a drive source may also be used as other filter movingmeans than the water current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away schematic perspective view of thecirculating filter type sewage disposal apparatus according to a firstembodiment of the invention;

FIG. 2 is a schematic plan view of the apparatus from the view II ofFIG. 1;

FIG. 3 is a schematic cross section of the apparatus taken along theline III--III of FIG. 2;

FIG. 4 is a schematic cross section of the apparatus taken along theline IV--IV of FIG. 2;

FIG. 5 is a schematic cross section of the apparatus taken along theline V--V of FIG. 2;

FIG. 6 shows schematically of the circulating filter type sewagedisposal apparatus according to a second embodiment of the invention inthe cross section corresponding to that of FIG. 4;

FIG. 7 is a schematic plan view of the circulating filter type sewagedisposal apparatus according to a third embodiment of the invention; and

FIG. 8 is a schematic cross section taken along the line VIII--VIII ofFIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to the attached drawings.

It should be appreciated that like or corresponding parts arerepresented by the same reference numbers, and duplicate descriptionthereof will be omitted.

While the following embodiments are all described referring to aerobictype, the present invention is not limited thereto, but may be appliedto those of anaerobic type.

First Embodiment

A circulating filter type sewage disposal apparatus 1 according to afirst embodiment of the invention consists of a septic tank 2 containingfilter media A, and a circulating means 3 for circulating the filtermedia A in the septic tank 2, as shown in FIG. 1.

As will be obvious from the later description, the filter media A in theseptic tank 2 must be buoyant ones, for example, having a specificgravity of 0.95 to 0.98, which is slightly smaller than that of sewage,and an appropriate buoyancy such that they can float in the sewage, andalso they must be hard to agglomerate one another. Meanwhile, the filtermedia A each have a spherical form with a diameter of about 10 cm,preferably 10 to 12 cm, and more preferably they each consist of amultiplicity of frames so as to obtain larger surface area. As thefilter media A having such characteristics, the spherical filter mediumdisclosed in Japanese Patent No. 1343032 (Japanese Patent Publication(Kokoku) No. 61-2440) which has already been incorporated herein asreference is the most preferred.

Such filter media A, charged in the septic tank 2, pack intimately alongthe water surface M and downward to form an assembly of the filter mediaA, i.e. filter bed B. The sewage is purified by the action of theaerobic bacteria proliferating on the filter bed B. The filter media Aare preferably charged to the septic tank 2 in an amount of 55 to 60% ofthe sewage accepting volume thereof.

The septic tank 2 is of an elongated rectangular shape, for example,having a length of 60 m and a width of 30 m. An upstream side wall 2ahas a sewage inflow port 5 at the upper portion thereof, and a purifiedwater discharge pit 7 is defined at one corner by a partition 6 on thedownstream side. The sewage flowed through the sewage inflow port 5 istreated by the filter bed B as it flows gently downstream in contactwith the filter bed B to be finally purified before it reaches thedownstream extremity, and the purified water flows through amultiplicity of through holes 8 formed on the partition 6 into thepurified water discharge pit 7 and is discharged therefrom by pumpingup. It should be noted that the partition 6 defining the purified waterdischarge pit 7 also plays a role of eliminating dead area in the"movement" (to be described later) of the filter media A or filter bedB.

The filter circulating means 3 is intended for circulating the filtermedia A by repeating continuously the operation of returning the filtermedia A separated from the filter bed B at the downstream extremity ofthe septic tank 2 to the filter bed B at the upstream extremity, wherebyto allow the filter bed B as a whole to flow calmly downstream as if itwere a glacier. The clogging of the filter media A can effectively beprevented by the flow of the filter bed B. In order to provide such flowof the filter bed B, the filter circulating means 3 consists of acirculation passage 9, a filter moving current forming means 10, a firstcurrent forming means 11 and a second current forming means 12.

The circulation passage 9 is a means for moving the filter media A fromthe downstream side to the upstream side, which has a width W slightlylarger than the diameter of the filter medium A and a depthsubstantially equal to that of the septic tank 2, and is provided alongone longitudinal side of the septic tank 2, with one end portion thereofcommunicating through an inlet 13 to the downstream extremity of thetank 2, while the other communicating through an outlet 14 to theupstream extremity of the septic tank 2. The inlet 13 is defined bycutting off a part of the upper portion of the side wall 2b and has adepth D (measured from the water level) of 2 to 3 times the diameter ofthe filter medium A. Namely, such depth of the inlet 13 in combinationwith the width of the circulation passage 9 can introduce one to severalfilter media A at one time from the upper layer of the filter bed B tothe circulation passage 9. Meanwhile, the outlet 14 is defined at thedownstream end portion of the circulation passage 9 to communicate tothe inside of the septic tank 2, in the minimum size necessary forallowing the filter media A to return into the septic tank 2. Morespecifically, the outlet 14 is defined at the upper part of a partitionmember 14w provided at the downstream end portion of the circulationpassage 9, and has a height of about 2 to 3 times the diameter of thefilter medium A. The outlet 14 has a triangular prismatic guide plate 15disposed adjacent thereto so as to eliminate the dead area in the"movement" of the filter media A or filter bed B.

The filter moving current forming means 10 is intended for forming acurrent, in the circulation passage 9, which flows from the downstreamextremity to the upstream extremity of the septic tank 2, and suchcurrent can be formed by jetting out the treated water in the purifiedwater discharge pit 6 into the circulation passage 9 using a pump (notshown). The filter media A introduced from the inlet 13 are adapted toflow on this current formed by the filter moving current forming means10 and moved from the downstream extremity to the upstream extremity ofthe septic tank 2. Incidentally, while the filter media A arespontaneously introduced to the circulation passage 9 due to theinfluence of the current exerted around the inlet 13 communicating tothe septic tank 2, bridging of filter media A may occur around the inlet13 depending on the conditions. Accordingly, it is preferred to providea suitable means such as an impeller, which rotates slowly, at the inlet13 to feed forcedly the filter media A into the circulation passage 9.

The jetting power and the position of the nozzle 10n of the filtermoving current forming means 10 are set to predetermined levels,respectively, so that it can form a vortex current 16 parallel to thelength and depth of the circulation passage 9. The vortex current 16serves as a means for removing sludge from the filter media A. Namely,the filter media A moving along the circulation passage 9 on the currentare also involved in the vortex current 16 and rotated, whereby thesludge deposited on the filter media A can be removed to clean thefilter media A. The sludge flakes released from the filter media A creepalong the slanted bottom of the circulation passage 9, accumulates in apit 17 and is recovered by a pump (not shown).

Use of such water current system circulation passage 9 as the filtermoving means facilitates separation of the filter media A from thefilter bed B more effectively and efficiently and also reduces possiblecauses of troubles in the filter moving means. However, the filtermoving means is not limited to the water current system, and, forexample, a conveyor having a drive source, as necessary, equipped with asuitable sludge removing means thereon may be used. If the currentsystem is employed, the intended object can fully be attained byproviding a circulation passage having a depth so as to allow movementof the filter media A in one row therethrough. As such circulationpassage, a ready-made concrete pipe may be disposed in the septic tank.

If a sludge removing means is provided in the circulation passage 9, thetreated water is prevented from being affected by the sludge coming offfrom the filter media, and thus purification efficiency can further beenhanced. Further, the use of the vortex current 16 can provide a verysimple and efficient sludge removing means. It is not always necessaryindeed to provide such sludge removing means, since clogging of thefilter media A can fully be prevented basically with the aid of the flowof the filter bed B, as described above, and if necessary other suitablemeans than the vortex current 16 can also be employed.

The first current forming means 11 is a part of the means for returningthe filter media A moving along the circulation passage 9 to the filterbed B and is disposed at the upstream extremity of the septic tank 2,more specifically adjacent to the outlet 14 of the circulation passage9.

The first current forming means 11, like the filter moving currentforming means 10, jets out the treated water introduced from thepurified water discharge pit 6 at a position rather closer to the waterlevel M and forms a vortex current 18 orthogonal to the length of theseptic tank 2 and parallel to the depth thereof. The filter media A fedout of the outlet 14 of the circulation passage 9 are involved in thisvortex current 18 and rotate, and thus they are ready to be returned tothe filter bed B. Simultaneously, this rotational movement of the filtermedia A involved in this current 18 allows cleaning of the filter mediaA, as it happens in the circulation passage 9, whereby clogging of thefilter media A can be prevented effectively. The sludge flakes releasedfrom the filter media A creep along the slanted bottom of the septictank 2, as it happens in the case of circulation passage 9, accumulatein a sludge pit 19 and are recovered by a pump (not shown).

The second current forming means 12 is intended for returning therotating filter media A involved in the vortex current 18 formed by thefirst current forming means 11 to the filter bed B, and is disposed tooppose diagonally to the first current forming means 11 at the cornerspace defined by a guide plate 21 for eliminating the dead area, like inthe case of guide plate 15. The second current forming means 12 forms astraight jet stream current 20 toward the downstream side of the septictank 2 from a corner at the upstream extremity thereof. The filter mediaA involved in the vortex current 18 are driven out therefrom by thestraight jet stream current 20 and returned to the bottom layer of thefilter bed B.

Incidentally, the septic tank has at the bottom thereof a grate forpreventing the filter media A from sinking to the bottom when the septictank 2 is emptied and an aeration pipe for feeding air. Since thesemembers are of well known structures, description thereof will beomitted. For easier understanding, the ratios of the size of the septictank 2 to the filter media A and to other members are convenientlymodified in the drawings.

Second Embodiment

In the second embodiment, a plurality of sludge removing means whichform vortex currents 16 are provided in the circulation passage 9, asshown in FIG. 6. This embodiment is suitably employed in the case of anelongated septic tank.

Third Embodiment

In the third embodiment, the septic tank 32 is of a shuttle typestructure, as shown in FIGS. 7 and 8. More specifically, a partition 33is disposed along the center line of the septic tank 32 to define aU-shaped passage, in which the upstream extremity and the downstreamextremity are located side by side. This structure is suitably employedin the case of an elongated septic tank and allows effective utilizationof the installation space.

In such shuttle type septic tank, a conveyor 34 may be disposed as thefilter moving means across the adjacent upstream extremity anddownstream extremity. The same effect as in the first embodiment can beobtained by transferring the filter media A reached the lower extremityto the upstream extremity as carried on the conveyor 34 and returningthe thus transferred filter media A to the bottom layer of the filterbed B using the same first current forming means 11 and the secondcurrent forming means 12 as in the first embodiment.

CAPABILITY OF EXPLOITATION IN INDUSTRY

In the circulating filter type sewage disposal apparatus according tothe present invention, the filter media are circulated by a circulationmeans to provide a gentle flow of filter bed, so that clogging of thefilter media can be prevented effectively. Since the sludge deposited onthe filter media are adapted to be removed by utilizing the circulatorymovement of the filter media, prevention of filter medium clogging canbe achieved more effectively. Besides, such prevention of filter mediumclogging is carried out without affecting the sewage under purificationtreatment, contributing greatly to the improvement of purificationefficiency of filter system sewage disposal treatment.

What is claimed is:
 1. A circulating filter type sewage treatmentapparatus, comprising:a septic tank having an upstream extremity, adownstream extremity and a multiplicity of buoyant filter mediaaccommodated therein to form a filter bed in which sewage flowsdownstream; a filter moving means for returning the filter media to theupstream extremity from the downstream extremity of the septic tank; anda first current forming means at the upstream extremity of the septictank for generating a vortex current and a second current forming meansat the upstream extremity of the septic tank for generating a straightjet stream current; wherein filter media separated from the filter bedat the downstream extremity of the septic tank are brought back to theupstream extremity of the septic tank by the filter moving means, whilefilter media brought back to the upstream extremity are returned to thebottom layer of the filter bed by the vortex current from the firstcurrent forming means and the straight jet stream current from thesecond current forming means.
 2. The circulating filter type sewagetreatment apparatus according to claim 1, wherein said filter movingmeans is a current flowing from a downstream side to an upstream side ofthe septic tank, formed in a circulation passage defined in the septictank which communicates at one end portion to the downstream extremityof the septic tank at the other end portion to the upstream extremitythereof.
 3. The circulating filter type sewage treatment apparatusaccording to claim 2, wherein said circulation passage has providedtherein a sludge removing means for removing sludge from the filtermedia.
 4. The circulating filter type sewage treatment apparatusaccording to claim 3, wherein said sludge removing means is a vortexcurrent formed in the circulation passage.
 5. The circulating filtertype sewage treatment apparatus according to claim 3, wherein saidsludge removing means is a series of vortex currents disposed along alength of said circulation passage.
 6. The circulating filter typesewage treatment apparatus according to claim 1, wherein said septictank is of a shuttle type structure where the upstream extremity and thedownstream extremity are located side by side.
 7. The circulating filtertype sewage treatment apparatus according to claim 6, wherein saidfilter moving means is a conveyor having a drive source.
 8. Thecirculating filter type sewage treatment apparatus according to claim 7,wherein said first current forming means for generating a vortex currentcomprises a first water jet adjacent an outlet of said conveyor, andsaid second current forming means for generating a straight jet streamcurrent comprises a second water jet disposed at a lower level than saidfirst water jet.
 9. The circulating filter type sewage treatmentapparatus according to claim 1, wherein said filter moving means is aconveyor having a drive source.
 10. The circulating filter type sewagetreatment apparatus according to claim 1, wherein said first currentforming means for generating a vortex current comprises a first waterjet disposed adjacent an upstream end of said circulation passage, saidfirst water jet having an outlet directed generally perpendicular to adownstream direction of the septic tank.
 11. The circulating filter typesewage treatment apparatus according to claim 10, wherein said secondcurrent forming means for generating a straight jet stream currentcomprises a second water jet disposed adjacent an opposite side of theseptic tank with respect to said first water jet, said first water jethaving an outlet directed generally in a downstream direction.
 12. Thecirculating filter type sewage treatment apparatus according to claim11, wherein the outlet of said first water jet is at a higher level thanthe outlet of said second water jet.
 13. The circulating filter typesewage treatment apparatus according to claim 12, wherein a partitionmember is provided at said upstream end of said circulation passage,said partition member blocking a lower portion of the circulationpassage to direct filter media to the first water jet and to preventsludge from recirculating back through the septic tank.
 14. Thecirculating filter type sewage treatment apparatus according to claim13, wherein a bottom surface of said circulation passage is sloped in adirection of a first sludge accumulating pit adjacent said partitionmember.
 15. The circulating filter type sewage treatment apparatusaccording to claim 14, wherein a bottom surface of the septic tankadjacent said upstream extremity is sloped in the direction of a secondsludge accumulating pit adjacent said second water jet.